I'm confused with you P_O. I would think that from the instructions you lose one (1) stitch when you k2tog and you lose another stitch (2) if you pass the previous slipped stitch over the k2tog, therefore if you repeat this action twice you remove a total of 4 stitches.
I looked up the abbreviation "PS" on the web (http://www.knittingfool.com/pages/ab...=201&PageNum=6
) and it says that PS stands for "patent stitch" (I've never heard of this stitch maneuver). Maybe you should try it, the instructions say you are supposed to slip 1 stitch with the yarn forward and bring the yarn over the needle. Doing PS this way allows you to replace one decrease and or removed stitch with a yarn over.
Or maybe it's a typo and you are supposed to simply purl the following stitch after you k2tog and I am making it more complex than it needs be.
HTH. If possible, could you let us know how it works out.